Trace and contextual fear conditioning were evaluated in adult (3-6 months), early middle-aged (8-12 months), late middle-aged (16-20 months), and aged (24-33 months) Sprague-Dawley rats. After trace conditioning, aged animals exhibited significantly less freezing to the tone conditioned stimulus and training context. Levels of trace-cue and context conditioning were negatively correlated with age (r = -0.56 and -0.59, respectively) and positively correlated with each other (r = +0.52). Aged rats showed robust conditioning in short- and long-delay fear paradigms, suggesting that the trace interval, rather than the use of a long interstimulus interval, is responsible for the aging-related deficits in trace fear conditioning. The authors suggest that these aging-related conditioning deficits furnish useful indices of functional changes within hippocampus or perirhinal cortex.
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